Ducted fans as used in gas turbine engines of the type known as fan-jets

ABSTRACT

A ducted fan having more than one blade row has bleed means adjacent the tips of the blades in at least one upstream blade row. The bleed means are preferably connected by passages to a compressor, the compressor being separate from but driven by a gas generator with which the ducted fan is combined to provide a fan jet engine. Alternative forms of the invention also have bleed means adjacent the roots of the blades in at least one upstream blade row, and there may also be bleed means adjacent the trailing edges of the blades in such rows.

United States Patent Howell 51 May 29, 1973 [541 DUCTED FANS AS USED INGAS 2,618,433 11/1952 Loos et al ..415/115 TURBINE ENGINES 0F THE TYPE3,494,129 2/1970 Krebs et al. ..4l5/l44 KNOWN AS FANJETS 3,572,960 31971 McBride ..4l5/DIG. 1 3,447,74l 6/1969 Hayette HMS/DIG l 1 lnventorIAlun Raymond Howell, Cove, Farn- 3,632,223 1/1972 Hampton ..41s/144borough, England [73] Assignee: Minister of Aviation Supply in HerPrimary EXami'lerA1LaWTve ne Smith B i i M j Governmem f AssistantExaminerWarren E. Olsen th U it d Ki d f Great B it i AttorneyCameronKerkam and Sutton,- Stowell & and Northern Ireland, London, En- S gland[22] Filed: Feb. 11, 1971 [57] ABSTRACT A ducted fan having more thanone blade row has [21] Appl' 1l4469 bleed means adjacent the tips of theblades in at least [30] Foreign-Application Priority Data one upstreamblade row. The bleed means are preferably connected by passages to acompressor, the Feb. ll. l970 Great Britain 6498/70 compressor beingseparate from but driven by a gas generator with which the ducted fan iscombined to [52] US. Cl. ..60/226, 415/115, 415/144 provide a fan jetengine. Alternative forms of the i Int- 6 v ention also have bleed meansadjacent the roots of [58] Field of Search ..4l5/79, 115, 119, theblades i at least one upstream blade row and 415/144 DIG-1; 60/226 theremay also be bleed means adjacent the trailing edges of the blades insuch rows. [56] References Cited 14 Claims, 6 Drawing Figures UNITEDSTATES PATENTS 2,692,724 10/1954 McLeod ..60/226 2,848,155 8/1958Hausmann ..4l5/l44 In at n PATENTED MAY 2 91975 sum 3 n 3 DUCTED FANS ASUSED IN GAS TURBINE ENGINES OFTI-IE TYPE KNOWN AS FAN-JETS Thisinvention relates to ducted fans as used in gas turbine engines of thetype known as fan-jets. In" such engines. only a proportion of airpassing through the fan passes through the gas generator. It is usuallyfound necessary, to minimize swirl in the air leaving the fan, to have astator blade row associated with each fan rotor row. In passing eachblade row turbul'ence is-imparted to the airflow, and this turbulenceinteracts with any downstream blade row to create noise whichcontributes significantly to total engine noise. One form of turbulenceis vortices which issue from the tips and roots of the blades, andreducing these vortices will reduce the total engine noise. Reducing thevortices will also improve the efficiency of the fan, though theefficiency of the engine will also be affected by the power used toreduce the vortices, and thenet result may be adverse to overall engineefficiency. Most of the benefit will follow from reducing the' vorticesat the tips of the blades.

It is an object of this invention to reduce tip and, in some cases, rootvortices extending from upstream blade rows in the fan section of a fanjet engine.

According to the invention, a ducted fan having more than one blade rowin'the fan section has bleed means adjacent tipsof blades in at leastone upstream blade o I l l According to another form of the invention, aducted fan having more than one blade row in the fan section has bleedmeans adjacent roots and tips of blades in at least one upstream bladerow.

i the application of the invention to fan jet engines theble'ed meansare connected to passages preferably leading to a compressor. Bleedpassages from the blade tips may pass through hollow stator blades, andthe compressor maybe driven by and exhaust into the gas generator.

Air may also be drawn from orifices adjacent the trailingedges of theblades to reduce trailing edge vortice's.

Some embodiments of the invention will now be described, by wayofexample' only, with reference to the accompanyingdrawings,"FIGS'. l'to6, each of which illustratesdiagrammatically and 'insection a differentfan and compressor system for a fan jet engine. Where appropriate, likeparts in the figures are referred to by the samereferenc e numbers.

FIG? l'shows 'a fan jet engine having a circumferential row Oran rotorblades, such as thatshown at 1. Each rotor blade '1 has a root la and atip lb, is mounted on one end of ashaft 2, and is rotatable within acylindricald uctdefined by an annular shroud casing 3.-A secondrotatable shaft 4, coaxial with and'surrounding the shaft 2, carries atone end a primary compresson'indicated by a row of rotor blades 5, and asecondary compressor indicated by the rows of rotor blades 6.' At theother ends of the shafts 2, 4 are turbine .unit'sfBetween the primarycompressor as indicated by therowof'ro'tor blades 5 and the turbineunits lie cornbustion units, the combination of compressor, combus tionunits and turbine units constituting a gas generatbr.

The primary and secondary compressor units are surrounded by twosections 7a and 7b respectively of a cylindrical casing. The radiallyouter surface of the casing Downstream, relative to the direction ofnormal flow through the duct as indicated by the arrow A, of the row offan rotor blades 1, secured between the casing 3 and the casing section7b, is a row of hollow stator blades such as that shown at 11. Thehollow interiors of the stator blades are connected by outlet passagessuch as that shown at 12 to the passage 9, and by inlet passages such asthat shown at 13 to an annular inlet 14 which is positioned in theradially inner surface of the casing 3 adjacent the tips lb of the fanrotor blades 1. Downstream of the row of stator blades 11, andseparating the casing sections 70, 7b is an annular inlet 15 which givesaccess via a passage 16 to the primary compressor. Rows of guide vanessuch as those indicated at- 17 guide air flowing through the passages9,16 onto the compressor rotor blades 6, 5.

To assist in reducing noise, various parts of the engine, as shown at18, may be made of silencing material, such as perforated panels orporous sheets backed by honeycomb structures to form single or multiplesandwiches.

In operation, the secondary compressor draws air from the boundary layeradjacent the roots 1a and tips lb of the fan rotor blades, thus reducingthe vorticity at these points. From the secondary compressor, air passesto the primary compressor, where it is joined by more air from the inlet15. The gas generator functions in the normal manner.

The arrangement shown in FIG. 2 differs from that shown in FIG. 1 inthat it has a row of narrow chord rotor blades, as shown at 21,connected together by a number of annular shrouds 22. The outer-mostshroud 22 lies in a recess 23 in the cylindrical casing 3, and therecess 23 connects with the passage 13. Each stator blade 11 has,adjacent its trailing edge, one or more orifices 24 connecting with thehollow interior. A final difference from the arrangement of FIG. 1 is,in the passage 9, a plurality of variable inlet guide vanes such as thatshown at 25, the disposition and degree of movement of these vanes beingsuch that the passage 9 may be completely sealed off. As in FIG. 1, therotor blades 21 are mounted on the outer end of fan rotor shaft 2 whilethe primary and secondary compressor blades 5 and 6am mounted on theouter end of shaft 4. The other ends of shafts 2 and 4 are connected toturbine units which, in combination with the compressor and combustionunits, constitute the gas generator.

In operation, the arrangement of FIG. 2 functions in a similar manner tothat of FIG. 1 when the vanes 25 are positioned to leave the passage 9open, with the addition that air is also drawn through the orifices 24,thus effecting a degree of boundary layer control and reducing thestrength of the trailing edge vortices which leave the stator blades 11.When thepassage 9 is sealed by the vanes 25, which may be desirableduring cruising flight and on occasions when noise reduction is not ofimportance, the gas generator will receive all its air through inlet 15.

FIG. 3 shows an arrangement having a row of fan rotor blades 31connected to annular shrouds 30a at the 'roots and 30b at the tips.Connecting the shroud 30a to a rotor disc 32 are compressor blades suchas that shown at 33a, and mounted on the shroud 30b are compressorblades such as that shown at 33b. The shroud 30a is rotatable insubstantially the same circumferential arc as an inner casing 7, therebeing an annular gap 34 betweenthe shroud and the casing. It will beseen that the blades 33a are thus aligned with a passage 9. Similarlythe blades 33b lie in a recess 23 in an outer casing 3 such that theyare aligned with a passage 13 in the outer casing, there being anannular gap 35 between the shroud 30b and the inner face of the casing3. The passage 13 connects, via hollow stator blades 11, with thepassage v9. The passage 9 leads to a compressor 5, and all the airsupply to the gas generator is supplied through the passage 9, therebeing no inlet similar to the inlet 15 of the arrangement shown in FIG.1.

In operation the pressure rise across the fan blades 31 will be greaterthan that across the compressor blades 33a, 33b, and boundary layer airwill thus bleed through the gaps 34, 35 into the passages 9, 13.Preferably, there should be more compressor blades 33b than fan blades31, in order to improve work capacity to help overcome the pressurelosses in the hollow stator blades 1 l.

The arrangement shown in FIG. 4 has hollow open ended fan blades such asthat shown at 41, the tips of the blades lying in a recess 43 inan'outer casing 3. Orifices 44 adjacent the trailing edges of the blades41 connect with the hollow interior. The hollow interiors of the blades41 are connected to a passage 9 by passages 42 in the rotor disc 40.Stator guide blades 11d are in this case solid. Otherwise, thisarrangement is similar to that shown in FIG. 2, variable inlet guidevanes 45 being provided in the passage 9 to enable this open ends of theblades. Also blade boundary layer air is drawn through the orifices 44,giving blade boundary layer control.

The arrangement shown in FIG. differs from that shown in FIG. 4 only inthat a secondary compressor 56 is mounted on the same shaft 52 as thehollow fan rotor blades 51. (In the arrangement shown in FIG. 4 thesecondary compressor is on the same shaft as the primary compressor.) Asthe rotational speed of the fan is less than that of the primarycompressor (not shown) the radius of the blade annulus of the secondarycompressor 56 is made as large as possible to give a sufficiently highperipheral blade speed.

The arrangement shown. in FIG. 6 is similar to that shown in FIG. 3 withthe following differences:

a. The air from the blade tips is passed to atmosphere through anannular diffusing passage 63, and

b. an additional auxiliary compressor stage 66 is mounted on a fan rotorshaft 62, and rotates in the passage 9.

It should be understood that although the above embodiments of theinvention are all front fan gas turbine engines, and have single row fanrotors with a stator row downstream of the rotor, the invention is notlimited to such arrangements. For example, it may beapplied to aft fanand other arrangements, and to engines having multi-stage fan rotors,and in cases where the most upstream blade row is a stator.

It should also beunderstood that the Figures are diagrammatic. Suchfactors as the disposition and number of primary compressor stator guideblades such as those shown at 17 in FIG. 1, and the number of secondarycompressor rotor rows, are matters of detail design:

for any particular engine. Although the primary corripressors as shownare single shaft systems, multi-shaft compressors may be used. The fanrotor may be driven by a turbine disc on its mounting shaft, or by agear box driven by a turbine of the gas generator.

The Figures and descriptions given refer to arrangements wherein thereare bleed means adjacent both tips and roots of fan blades, as this isthe most complicated form of the invention. It will be apparent,however, that these arrangements may be simply adapted to allow-forbleed means only at the tips of fan blades.

What I claim is:

1. In combination with a gas turbine engine of the type known as afan-jet engine having a gas generator, a ducted fan comprising:

at least one row of rotor blades mounted on a fan rotor shaft,

at least one row of stator blades, at least some of which are hollow,

an annular shroud enclosing said rows of rotor and stator blades andforming a duct for the passage of air, said rotor blades and said statorblades being axially spaced apart relative to the axis of the fan rotorshaft, I

annular bleed means adjacent the radially outermost tips of the bladesof at least one upstream blade row,

and a bleed compressor having an inlet and passages extending throughsaid hollow stator blades connecting said bleed means adjacent saidradially outermost tips to said inlet of said bleed compressor.

2. A ducted fan as claimed in claim 1 wherein a rotor of said bleedcompressor is connected so as to be directly driven by said gasgenerator.

3. A ducted fan as claimed in claim 2 wherein a rotor of said bleedcompressor is mounted on said fan rotor shaft.

4. A ducted fan as claimed in claim 3 wherein a rotor of said bleedcompressor is mounted on said fan rotor shaft.

5. A ducted fan as claimed in claim 1 further comprising a passageforming the inlet of said bleed compressor, and a plurality of variableguide vanes in said passage whereby the flow area of said passage can bevaried.

6. A ducted fan as claimed in claim 1 further comprising bleed meansadjacent the trailing edges of the blades of at least one blade row.

7. In combination with a gas turbine engine of the type known as afan-jet engine having a gas generator, a ducted fan comprising:

at least one row of rotor blades mounted on a rotor shaft, 1 atleast'one row of stator blades, at least some of which stator blades arehollow,

an annular shroud enclosing said rows of rotor and stator blades andforming a duct for the passage of air, said rotor blades and said statorblades b'eing axially spaced apart relative tothe axis shaft,

fan

of i the! fan rotor annular bleed means adjacent the radially outermostand the radially innermost tips of the blades of at least one upstreamblade row, 7 a bleed compressor having an inlet, passages connectingsaid bleed means adjacent said radially innermost tips to said inlet ofsaid bleed compressor, and passages extending through said hollow statorblades connecting said bleed means adjacent said radially outermost tipsto said inlet of said bleed compressor. 8. A ducted fan as claimed inclaim 7 wherein said gas generator has at least one compressor, and inwhich said bleed compressor is connected to exhaust into one of saidcompressors of said gas generator.

rotor of said bleed compressor is mounted on said fan rotor shaft.

11. A ducted fan as claimed in claim 8 wherein a rotor of said bleedcompressor is mounted on said fan rotor shaft.

12. A ducted fan as claimed in 8 further comprising a passage formingthe inlet of said bleed compressor, and a plurality of variable guidevanes in said passage whereby the flow area of said passage can bevaried.

13. A ducted fan as claimed in claim 7 wherein said bleed meanscomprises an annular diffusing passage in said annular shroud, leadingdownstream from adjacent said radially outermost tips to atmosphere.

14. A ducted fan as claimed in claim 7 further comprising bleed meansadjacent the trailing edges of the blades of at least one blade row.

1. In combination with a gas turbine engine of the type known as afan-jet engine having a gas generator, a ducted fan comprising: at leastone row of rotor blades mounted on a fan rotor shaft, at least one rowof stator blades, at least some of which are hollow, an annular shroudenclosing said rows of rotor and stator blades and forming a duct forthe passage of air, said rotor blades and said stator blades beingaxially spaced apart relative to the axis of the fan rotor shaft,annular bleed means adjacent the radially outermost tips of the bladesof at least one upstream blade row, and a bleed compressor having aninlet and passages extending through said hollow stator bladesconnecting said bleed means adjacent said radially outermost tips tosaid inlet of said bleed compressor.
 2. A ducted fan as claimed in claim1 wherein a rotor of said bleed compressor is connected so as to bedirectly driven by said gas generator.
 3. A ducted fan as claimed inclaim 2 wherein a rotor of said bleed compressor is mounted on said fanrotor shaft.
 4. A ducted fan as claimed in claim 3 wherein a rotor ofsaid bleed compressor is mounted on said fan rotor shaft.
 5. A ductedfan as claimed in claim 1 further comprising a passage forming the inletof said bleed compressor, and a plurality of variable guide vanes insaid passage whereby the flow area of said passage can be varied.
 6. Aducted fan as claimed in claim 1 further comprising bleed means adjacentthe trailing edges of the blades of at least one blade row.
 7. Incombination with a gas turbine engine of the type known as a fan-jetengine having a gas generator, a ducted fan comprising: at least one rowof rotor blades mounted on a fan rotor shaft, at least one row of statorblades, at least some of which stator blades are hollow, an annularshroud enclosing said rows of rotor and stator blades and forming a ductfor the passage of air, said rotor blades and said stator blades beingaxially spaced apart relative to the axis of the fan rotor shaft,annular bleed means adjacent the radially outermost and the radiallyinnermost tips of the blades of at least one upstream blade row, a bleedcompressor having an inlet, passages connecting said bleed meansadjacent said radially innermost tips to said inlet of said bleedcompressor, and passages extending through said hollow stator bladesconnecting said bleed means adjacent said radially outermost tips tosaid inlet of said bleed compressor.
 8. A ducted fan as claimed in claim7 wherein said gas generator has at least one compressor, and in whichsaid bleed compressor is connected to exhaust into one of saidcompressors of said gas generator.
 9. A ducted fan as claimed in claim 8wherein a rotor of said bleed compressor is connected so as to bedirectly driven by said gas generator.
 10. A ducted fan as claimed inclaim 9 wherein a rotor of said bleed compressor is mounted on said fanrotor shaft.
 11. A ducted fan as claimed in claim 8 wherein a rotor ofsaid bleed compressor is mounted on said fan rotor shaft.
 12. A ductedfan as claimed in 8 further comprising a passage forming the inlet ofsaid bleed compressor, and a plurality of variable guide vanes in saidpassage whereby the flow area of said passage can be varied.
 13. Aducted fan as claimed in claim 7 whErein said bleed means comprises anannular diffusing passage in said annular shroud, leading downstreamfrom adjacent said radially outermost tips to atmosphere.
 14. A ductedfan as claimed in claim 7 further comprising bleed means adjacent thetrailing edges of the blades of at least one blade row.